I expect 30 million+ for this, this game has a lot of good buzz going for it. Blackout has been met with positive reception and I feel like a lot of Twitch personalities will move over to this game. If this game also somehow becomes a Twitch mainstay which it totally can be, this will be the biggest COD in history.
PS4: 20 million
Xbox One: 12 million
PC: 6 million
Total: 38 million
It could be more, but I highly doubt it'll sell less than 30 million lifetime.